1. Field of Invention
The invention relates to a scanning module in a scanner.
2. Related Art
In addition to pictures, videos, multimedia, and computer briefing, daily business document processing also demands for digitalization of information. Although paperless offices have not realized yet, scanning has been used in businesses to reduce the use of paper.
The scanner has always been a useful input device. Its operation is very easy. One only needs to open the lid of the scanner, puts the original document on the glass, and covers the lid. The rest of the scanning task is done by using operating software to control the scanning module.
The basic principle of the scanner is to use a mechanical or electronic scanning module to read image points on a document and the convert them into digital information. Since the scanner converts the brightness of light cast from a light source and reflected by the image points on the original document, it is thus called the photoelectric conversion. During the process of the image sensor's reading the original document, light emitted from the light source is projected onto the surface of the document. The light reflected by the document passes lenses and forms an image on the sensor. Through the photoelectric conversion, an output voltage proportional to the concentration of the image is generated. The optical path can be controlled by the lenses.
In recent years, there is a trend to make all electronics as compact as possible, and so are scanners. As shown in FIG. 1, the lenses used in the scanning module 1 of a scanner are in a lens set 11 with a specific total track available on the market. The lens set 11 is provided with a circular lens (not shown). When using this lens set 11, the length L of the scanning module 1 has to be at least 250 mm. If one wants to shorten the total track, there will be distortion at the boundary of the image received by the image sensor 12 and the lens set 11 will have a larger size. Therefore, it is very difficult to minimize the volume of scanners.